May, 1953 
269 
Fig. 267.—Centroptilum walshi, male geni- 
talia. (After McDunnough.) 
Fig. 268.—Centroptilum rufostrigatum, male 
genitalia. 
Fig. 269.—Heteroclocon curiosum, male geni- 
talia. 
Mate.—Length of body and of fore wing 
6-7 mm. Head light yellow; scape and 
pedicel of each antenna yellow, flagellum 
gray-tan. Thorax tan, pleura faintly stained 
with red, sternum mostly yellow; legs light 
yellow, almost white, with each fore femur 
faintly stained with tan, and each fore tibia 
and tarsus slightly darkened with gray; 
wings hyaline, hind wing three and one-half 
times as long as broad. Entire abdominal 
Burks: THE MAyrFties oF ILLINOIS 121 
tergum, except for narrow area at lateral 
margins, uniformly shaded with dark red; 
abdominal venter faint yellow, almost white ; 
genitalia and caudal filaments white. 
Known from Alberta and Illinois. 
Illinois Record.—Carro: at light, July 
17;°1947,. L.. Jo Stannard, Ind. 
31. HETEROCLOEON McDunnough 
Heterocloeon McDunnough (1925b:175). 
In this genus, each fore wing has the 
marginal intercalary veins arranged in pairs. 
Each hind wing is reduced to a narrow, 
almost threadlike vestige which is either 
entirely without venation or with faint traces 
of a single longitudinal vein, and is also 
without a costal projection. The fore tarsus 
in the males is from one-half to two-thirds 
as long as the fore tibia. Each arm of the 
male genital forceps has four segments: the 
first segment is short and broad, with a 
small protuberance near the mediobasal 
angle; the second segment is narrower and 
conical; the third is long, slender, and bowed, 
with the medioapical angle produced; and 
the fourth segment is small, about two and 
one-half times as long as broad. The penis 
cover is emarginate on the meson, with each 
lateral angle conically produced. 
In the nymphs, the labial palp, fig. 261, 
has the suture between segments 2 and 3 
partly or completely obliterated and segment 
2 is not expanded at the mesoapical angle; 
the gills are single and platelike, with well- 
marked, pinnately branched tracheae; there 
are but two caudal filaments that are well 
developed. 
Heterocloeon curiosum (McDunnough) 
Centroptilum curiosum McDunnough 
(1923 :43). 
Heterocloeon curiosum (McDunnough). 
McDunnough (19254: 175). 
Baetis (Acentrella) curiosum (McDunnough). 
Ide (1937): 235). 
Mate—Length of body 4.5—-5.0 mm., of 
fore wing 5.0-5.5 mm. Head and thorax 
very dark brown to black; legs white, with 
the fore femur shaded with gray and all 
coxae dark brown; wings hyaline, stigmatic 
crossveins of fore wing partly anastomosed ; 
hind wing reduced to a narrow vestige, 
usually entirely without venation, but some- 
times with traces of one longitudinal vein. 
Abdominal segments 2-6 white, or stained 
